1. Technical Field
The present invention relates to an outlet cap adapted to be attached to the outlet of an on-off valve of a container containing a toxic gas.
2. Background Art
In production of semi-conductor devices such as LSI or ultra LSI, a toxic gas has been used at certain steps. For example, the process of conducting a thin-film deposition on a silicon wafer substrate consists of implanting or injecting a toxic gas such as arsine, phosphine, boron trifluoride as an ion source into semiconductors through an ion implanting apparatus to produce n-type and p-type semiconductors. Further, the process of dry-etching without the use of liquid such as etchant or solvent uses a toxic gas such as nitrogen trifluoride or hydrogen chloride as dry-etching agent.
Typically, a toxic gas is charged into a gas bomb or gas bottle made of iron or aluminum in order to put it on the market. Upon charging the toxic gas into the gas bottle, an outlet cap may be attached to the gas outlet of an on-off valve provided on the gas bottle.
Prior to the attachment of this outlet cap, the toxic gas which could exist within an interior space of the on-off valve must be exhausted for example, using a vacuum pump and then, the interior space of the on-off valve may be charged with an ambient air, nitrogen or the like. This is because if the outlet cap is removed from the gas outlet of the on-off valve for piping installation while the toxic gas could remain inside the on-off valve, the toxic gas will adversely diffuse from the on-off valve to the environment.
As a practical matter, however, it is difficult to perfectly empty the on-off valve of the toxic gas by the vacuum pump or the like. Further, the toxic gas may be temporarily adsorbed onto the inner metallic surfaces of the on-off valve defining the internal space thereof. In such a case, even if the toxic gas has been completely removed from the internal space of the on-off valve by the vacuum pump, the adsorbed toxic gas may be gradually released, thereby causing the internal space of the on-off valve to be filled with the toxic gas.
Therefore, the present invention was made to solve the problems and has its object to provide an outlet cap which can remove the toxic gas existing in the internal space of the on-off valve in the gas bottle.